Technical Field
The present invention relates to a power supply system including a first storage battery, a second storage battery, and a generator charging the first storage battery and the second storage battery.
Related Art
A power supply system for a vehicle is proposed in which a relatively inexpensive lead storage battery is used as a first storage battery, and a lithium-ion storage battery, which has energy efficiency in discharge and charge and energy density higher than those of a lead storage battery, is used as a second storage battery. In the system, the storage batteries are connected to a generator in parallel. For example, in JP-A-2007-46508, while an engine is driven, electrical power is supplied to an electric load (auxiliary unit) from a lead storage battery and a generator, and the lead storage battery and a lithium-ion storage battery are charged by the generator. While the engine is stopped, electrical power is supplied to the electric load (auxiliary unit) from the lithium-ion storage battery.
As described above, in the power supply system including a lead storage battery (first storage battery) and a lithium-ion storage battery (second storage battery), a battery unit is structured in which the lithium-ion storage battery and a controller controlling electric capacity of the lithium-ion storage battery are unitized. The battery unit is connected to the lead storage battery and the generator via connecting conductors (external unit wirings) such as a wiring harness. In this case, there is a concern that a fault such as a disconnection fault or a ground fault could occur in the connecting conductors. If a disconnection fault or a ground fault occurs in the connecting conductors, the lithium-ion storage battery cannot be charged. Thereby, electrical power cannot be supplied from the lithium-ion storage battery to the electric load, which is unintentional.
In addition, a fault of the power supply system other than the faults occurring in the connecting conductors (external unit wirings) such as a wiring harness outside the battery unit is considered to in possibly occur inside the battery unit. In this case, even if a fault occurs inside the battery unit, the lithium-ion storage battery cannot be charged. Thereby, it is possible that electrical power cannot be supplied from the lithium-ion storage battery to the electric load, which is unintentional.
When any fault occurs in the power supply system, and if it is erroneously determined that the battery unit is faulty even though the fault has occurred in the connecting conductors, the battery unit is unnecessarily changed or subjected to maintenance.